The one I have highlighted, although it says multiplied and divided by YA , but why in the formula its yA with t+1/ Y a with t?

goods where goods with a higher price or quantity get a bigger weight.\" We can see this more clearly by rewriting as follows: A s W. L + L- 1 ww+mw ww+rw _L_+L::u_l P\" Y" +P'Y' Y' P' Y" +P'Y' Y' ' In the second step_ we have multiplied and divided the " ' . . .. _ 'i'rhe last expression shows that real GDP growth is Cami3&3 as a weighted average of the growth of production of the two goods where the weights are the GDP shares of the goods in period t. This is reasonable since the GDP shares of the goods indicate how important the two goods are in production. Having done this calculation year by year we can construct a volume index of real GDP by starting from some base year where we set the index to 100, and then calculating an index for real GDP iteratively: YMI = (1 +5\") Yb An index calculated in this way is called a chain index. Note that the level of this index has no meaning; we can set it to 100 in some arbitrary year. What is interesting is how it changes over time